36 THE NATURE OF LIFE 



After repeated stimulation the organ- 

 ism shows signs of fatigue which disap- 

 pear after a sulBBcient period of rest. 

 Similar phenomena are observed in non- 

 living systems, as in an electric battery 

 which runs down somewhat during ac- 

 tivity but recovers on standing. In gen- 

 eral such effects are due to temporary 

 exhaustion of the available supply of en- 

 ergy or to the production of an inhibiting 

 substance which gradually disappears 

 during rest. 



It is often said that the response of 

 the organism differs from that of an in- 

 animate object, such as a billiard ball, 

 by being advantageous. 



It would be absurd to maintain that 

 all the acts of the organism are advanta- 

 geous. Numerous exceptions will be re- 

 called by all of us. Some actions which 

 seem advantageous on superficial exam- 

 ination may assume a different aspect on 

 more careful study. Putting such cases 

 aside there remain a large number which 

 are regarded by common consent as ad- 



